Population aging is currently a tough problem of many countries. How to utilize modern technologies (including both information and medical technologies) to improve the service quality of health information is an important issue. Personal Health Record (PHR) could be regarded as a kind of health information records of individuals. A ciphertext policy attribute-based encryption (CP-ABE) is a cryptographic primitive for fine-grained access control of outsourced data in clouds. In order to enable patients to effectively store his medical records and PHR data in medical clouds, we propose an improved multi-user CP-ABE scheme with the functionality of keyword search which enables data users to seek for specific ciphertext in the cloud server by using a specific keyword. Additionally, we adopt an independent proxy server in the proposed system architecture to isolate the communication between clients and the cloud server, so as to prevent cloud servers from suffering direct attacks and also reduce the computational loading of cloud servers. Compared with the previous approach, the proposed encryption algorithm takes less running time and the ciphertext length is also relatively short. Moreover, the procedures of re-encryption and pre-decryption only require one exponentiation computation, respectively.

IoT-based data outsourcing services in clouds could be regarded as a new trend in recent years, as they could reduce the hardware and software cost for enterprises and obtain higher flexibility. To securely transfer an encrypted message in the cloud, a so-called proxy re-encryption scheme is a better alternative. In such schemes, a ciphertext designated for a data aggregation is able to be re-encrypted as one designated for another by a semi-trusted proxy without decryption. In this paper, we introduce a secure proxy re-encryption protocol for IoT-based data outsourcing services in clouds. The proposed scheme is provably secure assuming the hardness of the bilinear inverse Diffie–Hellman problem (BIDHP). In particular, our scheme is bidirectional and supports the functionality of multi-hop, which allows an uploaded ciphertext to be transformed into a different one multiple times. The ciphertext length of our method is independent of the number of involved IoT nodes. Specifically, the re-encryption process only takes one exponentiation computation which is around 54 ms when sharing the data with 100 IoT devices. For each IoT node, the decryption process only requires two exponentiation computations. When compared with a related protocol presented by Kim and Lee, the proposed one also exhibits lower computational costs.